Optical View: Type I AGN:

Q2130-431

Q2130-431

Broad permitted lines Strong & variable continuum

Type II AGN:

Q2125-431

Q2125-431

Narrow forbidden & permitted lines Weak & constant continuum [Fig. from Hawkins 2004]

Unification Model

AGN intrinsically the same:

Basic Ingredients mass *Supermassive BH *Accretion disk + corona *BLR: high velocity, high density gas on pc scales *NLR; lower velocity, lower density gas on kpc scales *Torus: gaseous & molecular absorbing medium in equatorial plane embedding BH, ADC, BLR *Jets: relativistic ejection (10% AGN) Differences ascribed to viewing angle:

Type I Type II

Spectropolarimetry

Measure of polarization of light as a function of wavelengths

Instrumental in the development of Unification Model: Detection of broad permitted lines in polarized light in Sy2 NGC 1068 (Miller & Antonucci 1983) :

* presence of hidden BLR (HBLR)

* constraints on location and geometry of the absorber

But exceptions exist:

*Only 50% of Sy2 have HBLR (e.g. Tran 2001) based on 3-m (Lick) and 5-m (Palomar) telescopes

* Result confirmed by Keck 10-m telescope (Moran et al. 2007)

• Blazars – BL Lacs – OVV • Quasars – Radio Loud – Radio Quiet • Radio Galaxies – Narrow Line – Broad Line • Seyfert – Type 1 – Type 2

.Low Ionization Nuclear Emission-Line Regions (LINERS)

Radio galaxies

 associated to Elliptical galaxies

 Radiation power in radio area exceed the radiation power in the visual spectral area

Radio galaxy  They could be identified among other dimly objects in the visible light, because... − The galaxy in the visible light is not outshined by its core

nearest radio galaxy: Centaurus A (NGC 5128) Radio Sources

• Only few % of galaxies contain AGN • At low luminosities => radio galaxies

• Radio galaxies have powerful radio emission - usually found in ellipticals • RG 10 38 - 10 43 erg/s = 10 31 - 1036 J/s • Quasars 10 43 - 10 47 erg/s = 10 36 - 10 40 J/s

8 R Radio Galaxies

Optical image Radio image Centaurus A (“Cen A”): the most nearby AGN (3 - 4 Mpc).

.There is strong evidence that Centaurus A is a merger of an elliptical with a spiral galaxy, since elliptical galaxies would not have had enough dust and gas to form the young, blue stars seen along the edges of the dust lane. Radio Galaxies

Optical jet

Optical image Radio image

M 87: The central galaxy (giant elliptical galaxy) of the Virgo cluster of galaxies at a distance of 16 Mpc (redshift z=0.00436) Radio radiation

 The radio emission is synchroton radiation (emitted from electrons gyrating along magnetic field lines)

 The most common large-scale structures are called lobes: these are double, often fairly symmetrical structures placed on either side of the active nucleus.

In 1974, radio sources were divided by Fanaroff and Riley into two classes, now known as Fanaroff and Riley Class I (FRI), and Class II (FRII).

FRI FRII

A prototypical radio galaxy

Lobes

Core Hot-spots

Jets

. Any size: from pc to Mpc . First order similar radio morphology (but differences depending on radio power, optical luminosity & orientation) . Typical radio power 1023 to 1028 W/Hz

Radio Galaxies and Jets Cygnus-A → VLA radio image at -ν = 1.4.109 Hz (d = 190 MPc) 150 kPc

Radio Lobes

← 3C 236 Westerbork radio image ν 8 Radio Lobes at = 6.08.10 Hz – a radio galaxy of very large extent (d = 490 MPc) 5.7 MPc Jets, emanating from a central highly active galaxy, are due to relativistic electrons that fill the lobes 19 Cen A as an active galaxy is usually classified as a

. FR I type radio galaxy, . as a Seyfert 2 object in the optical (Dermer & Gehrels 1995), . . . and as a "misdirected" BL Lac type AGN at higher energies (Morganti et al. 1992).

It is one of the best examples of a radio-loud AGN viewed from the side ( ~ 70 degree) of the jet axis ( Graham 1979; Dufour et al. 1979; Jones et al. 1996).

Jets: Focussed Streams of Ionized Gas

lobe jet

energy carried out along channels material flows back towards hot galaxy spot

21 A prototypical radio galaxy

as ic g act gal ter d in backflow rbe bowshock istu und

as t g je ked hoc n” s coo “co

splash-point

What makes the difference?

Well known dichotomy: low vs high power radio galaxies

Differences not only in the radio

WHY? high-power radio galaxy

low-power Intrinsic differences in the radio galaxy nuclear regions? Accretion occurring at low rate and/or radiative efficiency? No thick tori? The Fanaroff-Riley Dichotomy

Is the dichotomy • Environmental? • Interaction of the jet with ambient medium either causes the jet to decelerate (FRI) or propagate supersonically to large distances (FRII) • Intrinsic? • Properties of the central engine govern large-scale morphology (FRI/FRII)

Radio Galaxies •Emit most of their energy at radio wavelengths •Emission lines from many ionization states •Nucleus does not dominate galaxy’s emission •Host galaxies are Elliptical/S0 Radio morphology first classified by Fanaroff & Riley (1974) •FR I: less luminous, 2-sided jets brightest closest to core and dominate over radio lobes •FR II: more luminous, edge-brightened radio lobes dominate over 1-sided jet (due to Doppler boosting of approaching jet and deboosting of receding jet)

Spectroscopic classification of radio galaxies •NLRGs (Narrow line …): like Seyfert 2s; FR I or II •BLRGs (Broad line …): like Seyfert 1s; FR II only

Different types of AGNs: a summary

Optical Emission Line Properties Type2 Type 1 Type 0 narrow line broad line

Radio quiet Seyfert 2 Seyfert 1

? Quasars Broad absorption line QSO Radio loud low power BL Lac Narrow-line OVV radio galaxies

high power broad-line RG lobe/core dominated QSR

Decreasing angle to line of sight Radio galaxies.:

These objects can broadly be divided into low-excitation (WLRG) and high-excitation classes (Hine & Longair 1979; Laing et al. 1994).

Low-excitation objects show no broad but also no strong-narrow emission lines, and the emission lines they do have (only weak narrow lines) may be excited by a different mechanism (Baum, Zirbel & O'Dea 1995).

Their optical and X-ray nuclear emission is consistent with originating purely in a jet (Chiaberge, Capetti & Celotti 2002; Hardcastle, Evans & Croston 2006).

They may be the best current candidates for AGN with radiatively inefficient accretion.

High-excitation classes By contrast, high-excitation objects (narrow-line radio galaxies) have emission-line spectra similar to those of Seyfert 2s.

The small class of broad-line radio galaxies, which show relatively strong nuclear optical continuum emission (Grandi & Osterbrock 1978) probably includes some objects that are simply low-luminosity radio-loud quasars.

The host galaxies of radio galaxies, whatever their emission-line type, are essentially always ellipticals.

http://www.vlti.org/events/assets/3/documents/torun2c.pdf Low- and High-Excitation Radio Galaxies Based on strength of high-excitation lines , e.g., [OIII] (Laing et al. 1994) • FRIs are almost entirely • Encompass all NLRGs low-excitation and BLRGs • Significant population of • Almost entirely FRIIs low-excitation FRIIs at 0.1

On small scales (< 15 kpc): 3 types of sources

Compact, Flat Spectrum (CFS) usually < 1”, physically small < 10 pc -α fν~ν , α~0 – 0.3 variable, polarized, superluminal on VLBI scales

Compact, steep spectrum (CSS) alpha = 0.7 – 1.2 sizes 1-20 kpc (within host galaxy) peak at < 500 MHz (limited by Ionospheric cutoff is at 10 MHz) 30% of cm-selected radio sources

GigaHertz Peaked Spectrum (GPS) radio spectrum peaks at 500 MHz to 10 GHz sizes < 1 kpc (within NLR) not very polarized alpha ~0.77 for E>E(peak) 10% of cm-selected radio sources

Bicknell + 1997 ApJ 485, 112

Spectral shape and Lifetimes Radio sources “age”  spectrum steepens Energy loss from radiation, adiabatic expansion

1/2 −1/2 Electron lifetime × 4 B [  ] t≃ 2. 6 10 2 2 1+ z ν b yr B + BR Break freq.

Equivalent magnetic field of the microwave background

Van der Laan & Perola 1969

GPS: B=10-3 G, nu_b=100 GHz  t=2000 years 100 Mhz  t=70,000 years

CSS: B=10-4 G, nu_b=100 GHz  t=70,000 years 100 MHz  t=2 million years “Compact Steep Spectrum” Radio Galaxies

• small radio sources (<1kpc) with steep spectral index: really small (no shortened by projection effects!) • Morphologically similar to kpc-Mpc double-sided radio galaxies (i.e. they have mini-lobes and/or jets on scales 1pc – 1kpc). The centre of activity, the “core” has an inverted radio spectrum and does not dominate the radio emission at cm wavelengths

They are considered to be newly-born radio galaxies

CSS

 Compact steep spectrum sources (=CSS) − ≤1“ in size, steep spectrum , peak at ca. ≤100 MHz – not visible − CSS sources are 10000-100.000 years old

CFS − Compact flat spectrum (=CFS) GPS

 Gigahertz peaked spectrum sources (=GPS) − Spectrum with convex form, peaks at ca. 1 Ghz − High frequency peakers (HFP)  Like GPS, peak at >5 Ghz

 GPS galaxies are young radio sources (~100- 1000 years old) CSS (compact steep spectrum) CFS (compact flat spectrum)

GPS (gigahertz peaked spectrum)

Different classifications. The same object! • Blazars – BL Lacs – OVV • Quasars – Radio Loud – Radio Quiet • Radio – Narrow Line – Broad Line • Seyfert – Type 1 – Type 2

What do we need to start a radio galaxy?

(or how do you make a black-hole active?) o Supermassive BH seem to be common among big early-type galaxies: but only a minority are active. o They need fuel! o Interactions/merger can bring gas to the central regions to feed the monster!

Possibility: the AGN-phase (including the radio activity) is only a “short” period in the life of a galaxy. Possibly, every galaxy goes through it.

Powerful radio galaxies

core dominated lobe dominated broad line

narrow line

 characteristics that are not orientation depended should be similar between powerful radio galaxies and quasars

Central

Quasars • Radio Quiet Quasars: – Strong emissions in both the optical and X-ray spectrums. – Within the optical spectrum, both broad and narrow emission lines are present, similar to a Type 1 Seyfert Galaxy. – Host is usually an elliptical galaxy. But less commonly, it might be a spiral. • Radio Loud Quasars: – All the same characteristics of a Radio Quiet Quasar with the addition of having strong radio emissions.

Quasars

• First discovered in the 1960s. • Detected radio sources with optical counterparts appearing as unresolved point sources. • Unfamiliar optical emission lines. • Maartin Schmidt was the first to recognize that these lines were normal Hydrogen lines seen at much higher redshifts than any previously observed galaxies. D = 660 Mpc (2.2 billion light years) for 3C273 1340 Mpc (4.4 billion light years) for 3C 48

13 L = 2 x 10 Lsun for 3C273. • Within ~2 years, quasars were discovered with: ≈ 14 z > 2 and L 10 Lsun • Most distant QSO discovered today - z = 6.42

λ emit wavelength emitted by the source

for motion solely in the line of sight (θ = 0°), this equation reduces to:

For v<

3C 273 is one of the closest quasars with a redshift, z, of 0.158 (spectral lines shifted to the red by 16 % ) It is also one of the most luminous quasars known, with an absolute magnitude of -26.7

Quasars

4 •MB < -23, strong nonthermal continuum, broad permitted (~10 km/s) and narrow forbidden (~102-3 km/s) emission lines

•Radio quiet (RQQ): elliptical or spiral host galaxies •Radio loud (RLQ): 5-10% of all quasars, elliptical hosts

•Broad Absorption Lines (BAL) Quasars: normal quasars seen at a particular angle along the l.o.s. of intervening, fast-moving material.

• High-ionization (HIBAL): Lyα, NV, SiIV, CIV • Low-ionization (LOBAL): AlIII, MgII

If we block out the light of luminous quasar, we can see evidence of an underlying host galaxy. Quasar hosts appear to be a mixed bag of galaxy types - from disturbed galaxies to normal E’s and early type spirals.

Quasars

9 M ~ 10 M BH Sun

13 L ~ 10 L = 100 L Quasar Sun Galaxy

Quasar Red Shifts

z = 0 z = 0.178 Quasars have been detected at the highest red shifts, z = 0.240 up to z ~ 6

z = 0.302

z = ∆λ/λ0 z = 0.389

Variability in AGNs

• QSOs and Seyfert nuclei have long been recognized as variable • Optical flux changes occur on timescales of months to years • Cause of variability? – instabilities in accretion disk, SN or starbursts, microlensing…..

Quasar light curve ~25 years Seyfert light curve over ~11 months

Hawkins 2002

Variability occurs at most wavelengths - X-rays through radio. This indicates that the fluctuations are originating from a very tiny object.

Why does rapid variability indicate small physical size of the emitting object?

Consider an object like the Sun. Any instantaneous flash ∆ would appear “blurred” in time by t = RSun / c.

RSun

observer RSun ∆ Time Delay = t = RSun / c 700,000 km / 300,000 km/s = 2.3 sec

Seyfert continuum luminosity varies significantly in less than a year (some variation occurs on timescales of days or weeks. This implies an emitting source less than a few light-weeks across!

Blazars

•Strongly variable, highly polarized nonthermal continua, weak/absent emission lines •Variability faster and higher amplitude than normal quasars and Seyferts •BL Lac - high polarization

•OVVs (Optically Violent Variables) - lower polarization, emission line EW decreases as continuum brightens

Spectrum Light Curve

* 'Blazars' (BL Lac objects and OVV quasars). These classes are distinguished by rapidly variable, polarized optical, radio and X-ray emission. BL Lac objects show no optical emission lines, broad or narrow, so that their redshifts can only be determined from features in the spectra of their host galaxies.

OVV quasars behave more like standard radio-loud quasars with the addition of a rapidly variable component.

In both classes of source, the variable emission is believed to originate in a relativistic jet oriented close to the line of sight. Relativistic effects amplify both the luminosity of the jet and the amplitude of variability.

BL-Lac objects  Firstly detected by Cuno Hoffmeister in 1929

 1968: detected as strong radio source

 Angle between jet axes and observing direction is very humble (direct view into the jet)

 Continuous spectrum without absorption- and emissionlines

 Strong emission in gamma-rays • Characteristics of both classes of Blazars: – Blazars are strong sources of high energy emissions (energies greater than 100 MeV). However they are luminous over the entire range of the spectrum, from radio up through gamma emission. – The host galaxies of Blazars are often Giant Elliptical galaxies.

Light curves of the Blazars BL Lac object 3C66A

Highest luminosities of all active galaxies

Variable on very short time scales (a few hours)

Sources of very strong X-ray and gamma-ray emission

Comparison of BL Lac and quasar Emission Lines:

BL Lac emissions shown on top, emission of a quasar shown below. Note: The BL Lac has no emission lines.

BL Lac

named after BL Lacertae, first identified example found in the constellation Lacerta and originally thought to be a variable star)

Wavelength (Angstroms) www.astro.isas.ac.jp/conference/bh2003/program/ppt/20031029am/KyotoBH2003_Falcke.ppt BL Lacs – A Pure Jet Spectrum

• BL Lacs are thought to be beamed Synchrotron Inverse FRI radio galaxies (low power!) from jetjet Compton • In BL Lacs the emission is from jetjet dominated by the jet due to relativistic beaming. • But there is also no evidence for any disk spectrum. • The jet spectrum resembles a „camel‘s back“. • Radio – optical – X-rays: synchrotron from jet • X-ray – TeV: inverse Compton from inner jet

– “Two-component” spectrum • Lo freq. peak ranges from < IR ⇒ X • Hi freq. peak at GeV ⇒TeV Fossati et al. (1998)

peak in mid-IR peak in EUV-X

FirstBright TeV-emitting EGRET-detected blazar: GeV-blazar: Mkn 421 3C279 ( (data from Macomb(Wehrle et al. 1995)1998) BLAZARS • “Two-component” spectrum – Lo freq. peak ranges from < IR ⇒ X – Hi freq. peak at GeV ⇒TeV

• Rapid variability – ~1 day with EGRET, limited by sensitivity – Shorter var. seen at TeV in brightest cases

•

Differences due to geometry: In the standard unification model for AGNs, a dusty torus covers a significant portion of the viewing angles to the accretion disk

Intrinsic differences: In X-ray binary sistems, the differences are due to variations in the accretion disk.

The same object! Different viewing angle to obscuring torus Face-on

• Blazars – BL Lacs – OVV • Quasars – Radio Loud – Radio Quiet • Radio n e-o – Narrow Line Edg – Broad Line • Seyfert – Type 1 – Type 2

X-ray intensity

http://www.mpifr-bonn.mpg.de/bonn04/presentations/koerding.pdf

Körding E. (2007) Ap&SS

Körding E. (2007) Ap&SS